Voltage regulator

Abstract

To adjust the balance of three-phase voltage at low cost.SOLUTION: A tap changing circuit 100 includes a mechanical switch 101 for switching the tap connected to a primary winding 21 of a series transformer 20 among a plurality of taps included in a secondary winding 32 of a regulating transformer 30. A semiconductor switching circuit 200 includes a semiconductor switch for switching the connection state of a tertiary winding 33 of the regulating transformer 30 to the primary winding 21 of the series transformer 20. The control circuit collectively controls the tap changing circuits 100 for the three phases to adjust the three-phase voltages collectively, and individually controls the semiconductor switching circuits 200 for the three phases to adjust the three-phase voltages individually.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a voltage regulator. [Background technology]

[0002] In recent years, with the spread of solar panels, electric vehicles, etc., it has become increasingly common for a large number of distributed power sources, single-phase loads, etc. to be connected to a power distribution system. As the number of distributed power sources, single-phase loads, etc. connected to a power distribution system increases, not only do the three-phase voltages of the power distribution system increase or decrease, but also three-phase voltage imbalances become more likely to occur. For this reason, there is currently a demand for technology that can adjust the three-phase voltages of a power distribution system to appropriate values.

[0003] Currently, step voltage regulators (SVRs) are known that adjust the three-phase voltage of a power distribution system by changing taps using mechanical switches. For example, Patent Document 1 describes an automatic voltage regulator that automatically adjusts the three-phase voltage by changing taps provided on an autotransformer using mechanical switches. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-55599 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the automatic voltage regulator described in Patent Document 1 adjusts three-phase voltages collectively. Therefore, although it can raise or lower three-phase voltages collectively, it is difficult to adjust the balance of the three-phase voltages. Also known is a thyristor voltage regulator (TVR), which adjusts the three-phase voltages of a distribution system individually by tap changing using thyristors. However, thyristors are more expensive than mechanical switches, and such TVRs are more expensive than the SVRs described above. Therefore, a technology for adjusting the balance of three-phase voltages at low cost is desired.

[0006] The present disclosure has been made in view of the above problems, and aims to provide a voltage regulator that adjusts the balance of three-phase voltages at low cost. [Means for solving the problem]

[0007] In order to achieve the above object, a voltage regulator according to the present disclosure includes: For each of the three phases in a distribution system that distributes three-phase voltage to loads, a series transformer having a primary winding and a secondary winding connected in series with the power distribution line; a regulating transformer including a primary winding connected to the distribution line, a secondary winding with multiple taps, and a tertiary winding connected in series with the primary winding and the secondary winding with multiple taps of the series transformer; a tap changing circuit including a mechanical switch for switching a tap connected to a primary winding of the series transformer among the plurality of taps provided on a secondary winding of the regulating transformer; a semiconductor switching circuit including a semiconductor switch for switching a connection state of a tertiary winding of the regulating transformer to a primary winding of the series transformer; The present invention is provided with a control circuit that collectively controls the tap changing circuits for three phases to adjust the voltages of the three phases, and that individually controls the semiconductor switching circuits for three phases to adjust the voltages of the three phases individually. [Effects of the Invention]

[0008] In the present disclosure, three-phase voltages are collectively adjusted by three-phase tap changing circuits equipped with mechanical switches, and three-phase voltages are individually adjusted by three-phase semiconductor switching circuits equipped with semiconductor switches. Therefore, according to the present disclosure, it is possible to adjust the balance of the three-phase voltages at low cost. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating a configuration of a voltage regulator according to an embodiment of the present invention; [Figure 2] An explanatory diagram of a voltage adjustment method according to an embodiment. [Figure 3] 1 is a diagram illustrating a configuration of a semiconductor switching circuit according to an embodiment of the present invention; [Figure 4] 1 is a diagram illustrating a semiconductor switching circuit according to a comparative example; [Figure 5] 1 is a flowchart showing a voltage adjustment process executed by a voltage adjustment device according to an embodiment. [Figure 6] 6 is a first flowchart showing the individual control process shown in FIG. 5. [Figure 7] 6 is a second flowchart showing the individual control process shown in FIG. 5. [Figure 8] Flowchart showing the collective control process shown in FIG. 5 DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings, in which the same or corresponding parts are designated by the same reference numerals.

[0011] (Embodiment) FIG. 1 is a diagram illustrating the configuration of a voltage adjustment device 1000 according to an embodiment. The voltage adjustment device 1000 adjusts three-phase AC voltage supplied from a power distribution system to a load. Main circuit wiring 10a, main circuit wiring 10b, and main circuit wiring 10c are wiring within the voltage adjustment device 1000 that connects to a distribution line for supplying three-phase AC voltage from the power distribution system to the load. The main circuit wiring 10a connects to a distribution line for supplying U-phase voltage. The main circuit wiring 10b connects to a distribution line for supplying V-phase voltage. The main circuit wiring 10c connects to a distribution line for supplying W-phase voltage. Hereinafter, the main circuit wiring 10a, main circuit wiring 10b, and main circuit wiring 10c will be collectively referred to as main circuit wiring 10, as appropriate. Furthermore, the voltage of each phase will be referred to as a phase voltage, and the voltage between each main circuit wiring 10 will be referred to as a line-to-line voltage, as appropriate.

[0012] Input terminals U1, V1, and W1 are input terminals of the voltage adjustment device 1000 and are terminals connected to the power distribution system. Output terminals U2, V2, and W2 are output terminals of the voltage adjustment device 1000 and are terminals connected to a load. The voltage adjustment device 1000 executes a collective control process, which is a control for collectively adjusting the U-phase, V-phase, and W-phase voltages, and an individual control process, which is a control for individually adjusting the U-phase, V-phase, and W-phase voltages.

[0013] Voltage adjustment device 1000 includes series transformer 20a, series transformer 20b, series transformer 20c, regulating transformer 30a, regulating transformer 30b, regulating transformer 30c, tap changing circuit 100a, tap changing circuit 100b, tap changing circuit 100c, semiconductor switching circuit 200a, semiconductor switching circuit 200b, semiconductor switching circuit 200c, voltage detection circuit 300, and control circuit 400. Hereinafter, series transformer 20a, series transformer 20b, and series transformer 20c will be collectively referred to as series transformer 20, as appropriate. Furthermore, regulating transformer 30a, regulating transformer 30b, and regulating transformer 30c will be collectively referred to as regulating transformer 30, as appropriate. Furthermore, where appropriate, tap changing circuits 100a, 100b, and 100c are collectively referred to as tap changing circuits 100. Furthermore, where appropriate, semiconductor switching circuits 200a, 200b, and 200c are collectively referred to as semiconductor switching circuits 200.

[0014] The series transformer 20 is a transformer provided in series with the main circuit wiring 10. The series transformer 20 is a compound-winding transformer having a plurality of windings. The series transformer 20 includes a primary winding 21 connected to the tap changing circuit 100 and the semiconductor switching circuit 200, and a secondary winding 22 connected in series with the main circuit wiring 10. More specifically, the series transformer 20a includes a primary winding 21a connected to the tap changing circuit 100a and the semiconductor switching circuit 200a, and a secondary winding 22a connected in series with the main circuit wiring 10a. The series transformer 20b includes a primary winding 21b connected to the tap changing circuit 100b and the semiconductor switching circuit 200b, and a secondary winding 22b connected in series with the main circuit wiring 10b. The series transformer 20c also includes a primary winding 21c connected to the tap changer 100c and the semiconductor changer 200c, and a secondary winding 22c connected in series to the main circuit wiring 10c.

[0015] The primary winding 21 is a collective term for the primary winding 21a, the primary winding 21b, and the primary winding 21c, and the secondary winding 22 is a collective term for the secondary winding 22a, the secondary winding 22b, and the secondary winding 22c. One end of the primary winding 21a is connected to the semiconductor switching circuit 200a, and the other end of the primary winding 21a is connected to the tap changing circuit 100a. One end of the primary winding 21b is connected to the semiconductor switching circuit 200b, and the other end of the primary winding 21b is connected to the tap changing circuit 100b. One end of the primary winding 21c is connected to the semiconductor switching circuit 200c, and the other end of the primary winding 21c is connected to the tap changing circuit 100c. One end of the primary winding 21a, one end of the primary winding 21b, and one end of the primary winding 21c are connected at a connection point P1. In other words, the three-phase primary windings 21 are connected in a star connection.

[0016] One end of the secondary winding 22a is connected to the input terminal U1, and the other end of the secondary winding 22a is connected to the output terminal U2. One end of the secondary winding 22b is connected to the input terminal V1, and the other end of the secondary winding 22b is connected to the output terminal V2. One end of the secondary winding 22c is connected to the input terminal W1, and the other end of the secondary winding 22c is connected to the output terminal W2.

[0017] The series transformer 20 has a function of superimposing an adjustment voltage on the main circuit wiring 10. Specifically, the series transformer 20 superimposes an adjustment voltage across the secondary winding 22 by applying a voltage regulated by the regulating transformer 30 to the primary winding 21. For example, the series transformer 20a superimposes an adjustment voltage across the secondary winding 22a by applying a voltage regulated by the regulating transformer 30a to the primary winding 21a.

[0018] The regulating transformer 30 is a transformer connected to the main circuit wiring 10 for regulating the three-phase AC voltage supplied to the load. The regulating transformer 30 is a compound-winding transformer having multiple windings. The regulating transformer 30 includes a primary winding 31 connected to the main circuit wiring 10, a secondary winding 32 with multiple taps, and a tertiary winding 33 connected in series with the primary winding 21 and the secondary winding 32 with multiple taps provided in the series transformer 20.

[0019] Specifically, the regulating transformer 30a includes a primary winding 31a connected to the main circuit wiring 10a, a secondary winding 32a with multiple taps, and a tertiary winding 33a connected in series with the primary winding 21a and the secondary winding 32a with multiple taps. The regulating transformer 30b includes a primary winding 31b connected to the main circuit wiring 10b, a secondary winding 32b with multiple taps, and a tertiary winding 33b connected in series with the primary winding 21b and the secondary winding 32b with multiple taps. The regulating transformer 30c includes a primary winding 31c connected to the main circuit wiring 10c, a secondary winding 32c with multiple taps, and a tertiary winding 33c connected in series with the primary winding 21c and the secondary winding 32c with multiple taps.

[0020] The primary winding 31 is a collective term for the primary winding 31a, the primary winding 31b, and the primary winding 31c; the secondary winding 32 is a collective term for the secondary winding 32a, the secondary winding 32b, and the secondary winding 32c; and the tertiary winding 33 is a collective term for the tertiary winding 33a, the tertiary winding 33b, and the tertiary winding 33c. One end of the primary winding 31a is connected to the output terminal U2, one end of the primary winding 31b is connected to the output terminal V2, and one end of the primary winding 31c is connected to the output terminal W2. The other end of the primary winding 31a, the other end of the primary winding 31b, and the other end of the primary winding 31c are connected at a connection point P3. In other words, the three-phase primary windings 31 are connected in a star connection.

[0021] The regulating transformer 30 generates, in the secondary winding 32 and the tertiary winding 33, a voltage whose magnitude corresponds to the magnitude of the voltage applied to the primary winding 31 and the turns ratio. When the winding directions of the secondary winding 32 and the tertiary winding 33 are the same, the turns ratio is the ratio of the number of turns of the primary winding 31 to the sum of the number of turns of the secondary winding 32 and the number of turns of the tertiary winding. When the winding directions of the secondary winding 32 and the tertiary winding 33 are opposite to each other, the turns ratio is the ratio of the number of turns of the primary winding 31 to the difference between the number of turns of the secondary winding 32 and the number of turns of the tertiary winding.

[0022] The tap changing circuit 100 changes the tap of the secondary winding 32 of the regulating transformer 30. The tap changing circuit 100 adjusts the voltage by an indirect adjustment method using the regulating transformer 30, which is a compound transformer. The tap changing circuit 100 includes a mechanical switch for switching the tap connected to the primary winding 21 of the series transformer 20 among multiple taps of the secondary winding 32 of the regulating transformer 30. The tap changing circuit 100 adjusts the turns ratio of the regulating transformer 30 by changing the tap of the secondary winding 32. For example, the tap changing circuit 100a adjusts the turns ratio of the regulating transformer 30a by changing the tap of the secondary winding 32a.

[0023] The tap changing circuits 100a, 100b, and 100c are collectively controlled by a control circuit 400. That is, the tap state of the secondary winding 32a, the tap state of the secondary winding 32b, and the tap state of the secondary winding 32c are always the same. For example, when the tap state of the secondary winding 32a is a state that maximizes the voltage generated in the secondary winding 32a, the tap state of the secondary winding 32b is a state that maximizes the voltage generated in the secondary winding 32b, and the tap state of the secondary winding 32c is a state that maximizes the voltage generated in the secondary winding 32c. The tap changing circuit 100 is, for example, a mechanical LTC (on-load tap changer).

[0024] The semiconductor switching circuit 200 switches the connection state of the tertiary winding 33 of the regulating transformer 30 between the primary winding 21 of the series transformer 20 and the secondary winding 32 of the regulating transformer 30. The semiconductor switching circuit 200 includes a semiconductor switch for switching the connection state of the tertiary winding 33 between the primary winding 21 and the secondary winding 32. The semiconductor switching circuit 200 regulates voltage by an indirect regulation method using the regulating transformer 30, which is a compound transformer. The semiconductor switching circuit 200 switches the connection state of the tertiary winding 33 by switching the state of the semiconductor switch, thereby adjusting the turns ratio of the regulating transformer 30. For example, the semiconductor switching circuit 200a switches the connection state of the tertiary winding 33a by switching the state of the semiconductor switch, thereby adjusting the turns ratio of the regulating transformer 30a.

[0025] Semiconductor switching circuits 200a, 200b, and 200c are individually controlled by control circuit 400. Semiconductor switching circuits 200a, 200b, and 200c are connected at connection point P2. That is, the semiconductor switching circuits 200 for three phases are connected by star connection.

[0026] The voltage detection circuit 300 is a circuit that detects three-phase AC voltages. The voltage detection circuit 300 is connected to the output terminal U2, the output terminal V2, and the output terminal W2. For example, the voltage detection circuit 300 detects Vuv, which is the line voltage between the output terminal U2 and the output terminal V2, Vvw, which is the line voltage between the output terminal V2 and the output terminal W2, and Vwu, which is the line voltage between the output terminal W2 and the output terminal U2. The voltage detection circuit 300 supplies information indicating the detected line voltages to the control circuit 400.

[0027] The control circuit 400 is a circuit that adjusts the three-phase AC voltage supplied to the load. The control circuit 400 adjusts the three-phase AC voltage supplied to the load by controlling the tap changing circuit 100 and the semiconductor switching circuit 200 based on the line voltage detected by the voltage detection circuit 300. The control circuit 400 performs a collective control process that adjusts the three-phase voltage collectively by collectively controlling the tap changing circuits 100 for the three phases. The control circuit 400 also performs an individual control process that adjusts the three-phase voltage individually by individually controlling the tap changing circuits 100 for the three phases. The control circuit 400 includes a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), RTC (Real Time Clock), etc.

[0028] Next, a voltage adjustment method using the voltage adjustment device 1000 will be described with reference to Fig. 2. In this embodiment, a method for adjusting the voltage superimposed on the main circuit wiring 10a using a tap changer circuit 100a and a semiconductor switching circuit 200a will be described. Using a similar method, the voltage superimposed on the main circuit wiring 10b can be adjusted using a tap changer circuit 100b and a semiconductor switching circuit 200b, and the voltage superimposed on the main circuit wiring 10c can be adjusted using a tap changer circuit 100c and a semiconductor switching circuit 200c.

[0029] The primary winding 21a of the series transformer 20a, the secondary winding 32a of the regulating transformer 30a, and the tertiary winding 33a of the regulating transformer 30a are connected in series to form a loop. The magnitude of the voltage applied to the primary winding 21a is proportional to the magnitude of the voltage applied to the primary winding 31a and the turns ratio of the regulating transformer 30a. The turns ratio of the regulating transformer 30a is calculated based on the connection state of the secondary winding 32a to the primary winding 21a and the connection state of the tertiary winding 33a to the primary winding 21a.

[0030] The connection state includes a positive connection state, a negative connection state, and a disconnected state. The positive connection state is a connection direction in which the phase voltage is increased. The negative connection state is a connection direction in which the phase voltage is decreased. The connection state of the secondary winding 32a to the primary winding 21a is controlled by tap switching using a tap changing circuit 100a. The connection state of the tertiary winding 33a to the primary winding 21a is controlled by switching the state of the semiconductor switch using a semiconductor switching circuit 200a.

[0031] In this embodiment, there are nine patterns for the connection state of the secondary winding 32a to the primary winding 21a. These nine patterns include a four-step step-up pattern for increasing the phase voltage, a pass-through pattern for not changing the phase voltage, and a four-step step-down pattern for decreasing the phase voltage. Also, in this embodiment, there are three patterns for the connection state of the tertiary winding 33a to the primary winding 21a. These three patterns include a step-up pattern for increasing the phase voltage, a pass-through pattern for not changing the phase voltage, and a step-down pattern for decreasing the phase voltage.

[0032] The tap changing circuit 100a includes a mechanical switch 101a for selecting one of nine taps. The mechanical switch 101a is a switch for connecting the primary winding 21a to one of the nine taps provided in the secondary winding 32a. The tap changing circuit 100b and the tap changing circuit 100c include a mechanical switch similar to the mechanical switch 101a. Hereinafter, these mechanical switches will be collectively referred to as the mechanical switch 101 where appropriate.

[0033] The semiconductor switching circuit 200a switches the state of the semiconductor switch to select one of three patterns: a boost pattern, a through pattern, and a step-down pattern. The boost pattern connects the tertiary winding 33a to the primary winding 21a in the positive direction so that the phase voltage increases. The through pattern does not connect the tertiary winding 33a to the primary winding 21a. The step-down pattern connects the tertiary winding 33a to the primary winding 21a in the negative direction so that the phase voltage decreases. As appropriate, operation using the boost pattern will be referred to as a boost operation, operation using the through pattern as a through operation, and operation using the step-down pattern as a step-down operation.

[0034] The configuration of semiconductor switching circuit 200 will be described below with reference to Fig. 3. As shown in Fig. 3, semiconductor switching circuit 200 includes semiconductor switch 211, semiconductor switch 212, semiconductor switch 213, semiconductor switch 214, semiconductor switch 220, resistor 230, and mechanical switch 240.

[0035] Semiconductor switch 211, semiconductor switch 212, semiconductor switch 213, semiconductor switch 214, and semiconductor switch 220 are semiconductor switches whose conduction state can be controlled by an electric signal, and in this embodiment, are switches configured by thyristors. Resistor 230 is a limiting resistor for limiting the flow of excessive current. Mechanical switch 240 is an electromagnetic contactor, and is a component that mechanically opens and closes contacts by electromagnetic action.

[0036] A series circuit of semiconductor switch 211 and semiconductor switch 212, a series circuit of semiconductor switch 213 and semiconductor switch 214, a series circuit of resistor 230 and semiconductor switch 220, and mechanical switch 240 are connected in parallel between primary winding 21 and secondary winding 32. Tertiary winding 33 is connected between the connection point of semiconductor switch 211 and semiconductor switch 212 and the connection point of semiconductor switch 213 and semiconductor switch 214.

[0037] The control circuit 400 controls the states of operation switches such as the semiconductor switch 211, the semiconductor switch 212, the semiconductor switch 213, the semiconductor switch 214, the semiconductor switch 220, and the mechanical switch 240, thereby controlling the voltage step-up / step-down operation by the semiconductor switching circuit 200. The voltage step-up / step-down operation includes three operations: a voltage step-up operation, a pass-through operation, and a voltage step-down operation.

[0038] The step-up operation is an operation in which the semiconductor switch 211 and the semiconductor switch 214 are turned on to connect the tertiary winding 33 to the primary winding 21 in the positive direction, thereby increasing the absolute value of the voltage across the primary winding 21. The pass-through operation is an operation in which the mechanical switch 240 is turned on to not connect the tertiary winding 33 to the primary winding 21, thereby leaving the absolute value of the voltage across the primary winding 21 unchanged. The step-down operation is an operation in which the semiconductor switch 212 and the semiconductor switch 213 are turned on to connect the tertiary winding 33 to the primary winding 21 in the negative direction, thereby decreasing the absolute value of the voltage across the primary winding 21.

[0039] If semiconductor switch 211, semiconductor switch 212, semiconductor switch 213, and semiconductor switch 214 are all turned off, the secondary circuit of semiconductor switching circuit 200 becomes open and an excessive voltage is generated. Therefore, when switching between boost and buck operation, control circuit 400 turns on semiconductor switch 220 to form a closed circuit in the secondary circuit via resistor 230, thereby suppressing the generation of excessive voltage.

[0040] For example, when switching from pass-through operation to boost operation, the control circuit 400 controls the operation switches in the following order: (A1) mechanical switch 240: on, (A2) semiconductor switch 220: on, (A3) mechanical switch 240: off, (A4) semiconductor switch 211, semiconductor switch 214: on, (A5) semiconductor switch 220: off.

[0041] Also, for example, when switching the boost operation to the pass-through operation, the control circuit 400 controls the operation switches in the following order: (B1) semiconductor switch 211, semiconductor switch 214: on, (B2) semiconductor switch 220: on, (B3) semiconductor switch 211, semiconductor switch 214: off, (B4) mechanical switch 240: on, (B5) semiconductor switch 220: off.

[0042] As described above, in this embodiment, the tap changing circuit 100, which is an LTC, a mechanical switching circuit used in SVR, can adjust the voltage of each phase collectively in nine steps, and the semiconductor switching circuit 200, which is a semiconductor switching circuit, can adjust the voltage of each phase individually in three steps. Here, the LTC can be implemented at low cost because it does not use semiconductor switches. Furthermore, the semiconductor switching circuit 200 can be implemented at relatively low cost because it is composed of a relatively small number of semiconductor switches.

[0043] Therefore, according to this embodiment, it is possible to individually adjust the voltage of each phase at low cost. Furthermore, because an SVR using an LTC can be realized at low cost, SVRs using LTCs are often incorporated into existing facilities. In this embodiment, the LTC and other components included in an existing SVR can be used. In other words, when using an existing SVR, it is possible to make very few changes to, for example, the interface specifications between the LTC and control circuit 400, and the interface specifications between the control circuit 400 and a higher-level control device.

[0044] On the other hand, instead of adding semiconductor switching circuit 200 to an existing SVR, a TVR including a semiconductor switching circuit that can adjust the voltage of each phase individually can be used. The switching circuit included in the TVR, i.e., semiconductor switching circuit 201 according to a comparative example, will be described below with reference to FIG. 4.

[0045] The regulating transformer 40 includes a primary winding 41 and a secondary winding 42. The semiconductor switching circuit 201 is a semiconductor-type switching circuit that can adjust the voltage of each phase individually. The semiconductor switching circuit 201 switches the state of a semiconductor switch connected to the secondary winding 42 included in the regulating transformer 40. The semiconductor switching circuit 201 switches the state of the semiconductor switch to switch the connection state of the secondary winding 42 to the primary winding 21, thereby adjusting the voltage across the primary winding 21 included in the series transformer 20.

[0046] In the comparative example, seven patterns are provided for the connection state of secondary winding 42 to primary winding 21, and seven levels of voltage adjustment are possible by switching the semiconductor switches using semiconductor switching circuit 201. In other words, in the comparative example, secondary winding 42 can be considered to have seven taps, and seven levels of voltage adjustment are possible by switching the taps using semiconductor switching circuit 201.

[0047] 4, semiconductor switching circuit 201 includes semiconductor switch 211, semiconductor switch 212, semiconductor switch 213, semiconductor switch 214, semiconductor switch 215, semiconductor switch 216, semiconductor switch 220, resistor 230, and mechanical switch 240. Semiconductor switch 215 and semiconductor switch 216 are semiconductor switches whose conduction state can be controlled by an electric signal, and in this embodiment, are switches formed by thyristors.

[0048] A series circuit of semiconductor switch 211 and semiconductor switch 212, a series circuit of semiconductor switch 213 and semiconductor switch 214, a series circuit of semiconductor switch 213 and semiconductor switch 214, a series circuit of resistor 230 and semiconductor switch 220, and mechanical switch 240 are connected in parallel across both ends of primary winding 21. One end of secondary winding 42 is connected to the junction of semiconductor switch 211 and semiconductor switch 212, a midpoint of secondary winding 42 is connected to the junction of semiconductor switch 213 and semiconductor switch 214, and the other end of secondary winding 42 is connected to the junction of semiconductor switch 215 and semiconductor switch 216.

[0049] The semiconductor switching circuit 201 selects one of seven voltage step-up / down operations, including three voltage step-up operations, a pass-through operation, and three voltage step-down operations. The three voltage step-up operations include an operation of turning on the semiconductor switches 211 and 216 to connect the entire secondary winding 42 to the primary winding 21 in the forward direction, an operation of turning on the semiconductor switches 211 and 214 to connect a part of the secondary winding 42 to the primary winding 21 in the forward direction, and an operation of turning on the semiconductor switches 213 and 216 to connect the remaining part of the secondary winding 42 to the primary winding 21 in the forward direction.

[0050] The pass-through operation is an operation in which the mechanical switch 240 is turned on to not connect the secondary winding 42 to the primary winding 21. The three-stage step-down operation includes an operation in which the semiconductor switch 212 and the semiconductor switch 215 are turned on to connect the entire secondary winding 42 to the primary winding 21 in the negative direction, an operation in which the semiconductor switch 212 and the semiconductor switch 213 are turned on to connect a part of the secondary winding 42 to the primary winding 21 in the negative direction, and an operation in which the semiconductor switch 214 and the semiconductor switch 215 are turned on to connect the remaining part of the secondary winding 42 to the primary winding 21 in the negative direction.

[0051] In the voltage regulator according to the comparative example, one semiconductor switching circuit 201 has seven semiconductor switches, making it difficult to realize at low cost. Furthermore, in the voltage regulator according to the comparative example, in seven-stage voltage regulation, in addition to adjusting the balance of the voltages of each phase, it is necessary to adjust the overall level of the voltages of each phase, for example, adjusting the average voltage of the voltages of each phase. Therefore, in the voltage regulator according to the comparative example, it is difficult to adjust the balance of the voltages of each phase with high resolution. Furthermore, in the voltage regulator according to the comparative example, if the semiconductor switching circuit 201 is provided with more semiconductor switches in order to be able to adjust the balance of the voltages of each phase with high resolution, the cost will further increase.

[0052] On the other hand, in this embodiment, one semiconductor switching circuit 200 has only five semiconductor switches, so it can be realized at low cost. Furthermore, in the voltage regulator 1000 according to this embodiment, the voltage of each phase can be adjusted collectively in nine stages, and the voltage of each phase can be adjusted individually in three stages. In this embodiment, all three stages of voltage adjustment can be allocated to adjusting the balance of the voltage of each phase. Therefore, in this embodiment, it is possible to adjust the balance of the voltage of each phase with high resolution.

[0053] Next, the voltage adjustment process executed by the voltage adjustment device 1000 will be described with reference to Fig. 5. The voltage adjustment process is executed continuously, for example, while the voltage adjustment device 1000 is powered on.

[0054] First, the control circuit 400 included in the voltage regulator 1000 measures V1, which is a line voltage (step S101). For example, the control circuit 400 controls the voltage detection circuit 300 to measure Vuv, Vvw, and Vwu. Vuv is the line voltage between the main circuit wiring 10a and the main circuit wiring 10b, and is the voltage between the U phase and the V phase. Vvw is the line voltage between the main circuit wiring 10b and the main circuit wiring 10c, and is the voltage between the V phase and the W phase. Vwu is the line voltage between the main circuit wiring 10c and the main circuit wiring 10a, and is the voltage between the W phase and the U phase. V1 is a collective term for Vuv, Vvw, and Vwu.

[0055] Upon completing the process of step S101, the control circuit 400 calculates V2, which is a phase voltage (step S102). For example, the control circuit 400 calculates Vu, which is a phase voltage of the U phase, Vv, which is a phase voltage of the V phase, and Vw, which is a phase voltage of the W phase, from Vuv, Vvw, and Vwu. Note that V2 is a general term for Vu, Vv, and Vw. Upon completing the process of step S102, the control circuit 400 determines the magnitude relationship between the voltages (step S103).

[0056] For example, the control circuit 400 compares Vuv, Vvw, and Vwu, and designates the highest line voltage as V1max, the middle line voltage as V1cen, and the lowest line voltage as V1min. The control circuit 400 also compares Vu, Vv, and Vw, and designates the highest phase voltage as V2max, the middle phase voltage as V2cen, and the lowest phase voltage as V2min. When comparing these voltages, for example, the average values ​​of the magnitudes of the three-phase voltages over the most recent specified time are compared. Similarly, when comparing voltages thereafter, these average values ​​are compared.

[0057] When the control circuit 400 completes the process of step S103, it executes individual control process (step S104). The individual control process is a process of individually controlling the three semiconductor switching circuits 200 and individually adjusting the phase voltage of each phase. The individual control process will be described below with reference to the flowcharts shown in FIGS. 6 and 7.

[0058] First, the control circuit 400 determines whether V2max-V2min≧Vth1 (step S201). Vth1 is the lower limit of the phase voltage difference that requires individual voltage adjustment. In other words, the control circuit 400 determines whether the difference between the highest and lowest phase voltages is large enough to require individual voltage adjustment. If the control circuit 400 determines that V2max-V2min≧Vth1 is not true (step S201: NO), it ends the individual control process.

[0059] If the control circuit 400 determines that V2max-V2min≧Vth1 (step S201: YES), it determines whether |V2max-V2cen|>|V2min-V2cen| (step S202). In other words, the control circuit 400 determines whether the imbalance in the phase voltages is caused by an overshoot of the highest phase voltage rather than a undershoot of the lowest phase voltage.

[0060] If the control circuit 400 determines that |V2max-V2cen|>|V2min-V2cen| (step S202: YES), it determines whether or not the V2max phase is under boost control (step S203). If the control circuit 400 determines that the V2max phase is under boost control (step S203: YES), it switches the V2max phase to through control (step S204), and then ends the individual control process.

[0061] When the control circuit 400 determines that the phase of V2max is not under boost control (step S203: NO), it determines whether or not the phase of V2max is under pass-through control (step S205). When the control circuit 400 determines that the phase of V2max is under pass-through control (step S205: YES), it switches the phase of V2max to step-down control (step S206) and then ends the individual control processing. In this way, when it is estimated that the phase voltages are unbalanced due to an overshoot of the highest phase voltage, the control circuit 400 reduces the voltage of the phase with the highest phase voltage if there is room to reduce the voltage of the phase with the highest phase voltage.

[0062] When the control circuit 400 determines that the V2max phase is not under pass-through control (step S205: NO), it determines whether the V2min phase is under step-down control (step S207).When the control circuit 400 determines that the V2min phase is under step-down control (step S207: YES), it switches the V2min phase to pass-through control (step S208) and then ends the individual control process.

[0063] When the control circuit 400 determines that the V2min phase is not under step-down control (step S207: NO), it determines whether the V2min phase is under through control (step S209). When the control circuit 400 determines that the V2min phase is under through control (step S209: YES), it switches the V2min phase to step-up control (step S210) and then ends the individual control processing. When the control circuit 400 determines that the V2min phase is not under through control (step S209: NO), it ends the individual control processing.

[0064] In this way, when it is estimated that the phase voltages are unbalanced due to an overshoot of the highest phase voltage, if there is no room to lower the voltage of the phase with the highest phase voltage, the control circuit 400 adjusts the voltage of the phase with the lowest phase voltage. Specifically, if there is room to increase the voltage of the phase with the lowest phase voltage, the control circuit 400 increases the voltage of the phase with the lowest phase voltage. On the other hand, if there is no room to increase the voltage of the phase with the lowest phase voltage, the control circuit 400 ends the individual control process without individually adjusting the voltage.

[0065] If the control circuit 400 determines that |V2max-V2cen|>|V2min-V2cen| is not true (step S202: NO), it determines whether or not the V2min phase is under step-down control (step S211). If the control circuit 400 determines that the V2min phase is under step-down control (step S211: YES), it switches the V2min phase to through control (step S212) and then ends the individual control process.

[0066] When the control circuit 400 determines that the V2min phase is not under step-down control (step S211: NO), it determines whether the V2min phase is under through control (step S213). When the control circuit 400 determines that the V2min phase is under through control (step S213: YES), it switches the V2min phase to step-up control (step S214) and then ends the individual control processing. In this way, when it is estimated that the phase voltages are unbalanced due to a downward fluctuation in the lowest phase voltage, and there is room to increase the voltage of the phase with the lowest phase voltage, the control circuit 400 increases the voltage of the phase with the lowest phase voltage.

[0067] When the control circuit 400 determines that the V2min phase is not under pass-through control (step S213: NO), it determines whether the V2max phase is under voltage boost control (step S215).When the control circuit 400 determines that the V2max phase is under voltage boost control (step S215: YES), it switches the V2max phase to pass-through control (step S216) and then ends the individual control process.

[0068] When the control circuit 400 determines that the V2max phase is not under boost control (step S215: NO), it determines whether the V2max phase is under pass-through control (step S217). When the control circuit 400 determines that the V2max phase is under pass-through control (step S217: YES), it switches the V2max phase to step-down control (step S218) and then ends the individual control process. When the control circuit 400 determines that the V2max phase is not under pass-through control (step S217: NO), it ends the individual control process.

[0069] In this way, when it is estimated that the phase voltages are unbalanced due to a downward swing in the highest phase voltage, if there is no room to increase the voltage of the phase with the lowest phase voltage, the control circuit 400 adjusts the voltage of the phase with the highest phase voltage. Specifically, if there is room to decrease the voltage of the phase with the highest phase voltage, the control circuit 400 decreases the voltage of the phase with the highest phase voltage. On the other hand, if there is no room to decrease the voltage of the phase with the highest phase voltage, the control circuit 400 ends the individual control process without individually adjusting the voltage.

[0070] Upon completing the individual control process of step S104, the control circuit 400 executes a collective control process (step S105). The collective control process is a process for collectively controlling the three tap changing circuits 100 and collectively adjusting the phase voltages of the respective phases. The collective control process will be described below with reference to the flowchart shown in FIG.

[0071] First, the control circuit 400 calculates V2ave, which is the average value of the phase voltages (step S301). After completing the process of step S301, the control circuit 400 determines whether V2ave≧Vth2 (step S302). Vth2 is the lower limit of the average value of the phase voltages at which a collective voltage drop is required. In other words, the control circuit 400 determines whether the average value of the phase voltages is large enough to require a collective voltage drop.

[0072] If the control circuit 400 determines that V2ave≧Vth2 (step S302: YES), it determines whether the current tap is the maximum step-down tap (step S303). The maximum step-down tap is the tap at which the magnitude of the phase voltage is smallest. In other words, the control circuit 400 determines whether there is room to reduce the magnitude of the phase voltage.

[0073] If the control circuit 400 determines that the current tap is not the maximum step-down tap (step S303: NO), it performs step-down control for all three phases collectively by one tap (step S304) and completes the collective control process. That is, the control circuit 400 switches the taps so that the magnitude of the phase voltage decreases by one step. Note that tap switching is performed collectively for all tap switching circuits 100. If the control circuit 400 determines that the current tap is the maximum step-down tap (step S303: YES), it completes the collective control process.

[0074] If the control circuit 400 determines that V2ave≧Vth2 is not true (step S302: NO), it determines whether V2ave≦Vth3 is true (step S305). Vth3 is the upper limit of the average value of the phase voltages that requires a collective voltage increase. In other words, the control circuit 400 determines whether the average value of the phase voltages is small enough to require a collective voltage increase. If the control circuit 400 determines that V2ave≦Vth3 is not true (step S305: NO), it ends the collective control process.

[0075] When the control circuit 400 determines that V2ave≦Vth3 (step S305: YES), it determines whether the current tap is the maximum boost tap (step S306). The maximum boost tap is the tap at which the phase voltage is at its maximum. In other words, the control circuit 400 determines whether there is any room to increase the phase voltage.

[0076] If the control circuit 400 determines that the current tap is not the maximum boost tap (step S306: NO), it performs boost control for one tap at a time for all three phases (step S307) and completes the collective control process. That is, the control circuit 400 switches the taps so that the magnitude of the phase voltage increases by one step. If the control circuit 400 determines that the current tap is the maximum boost tap (step S306: YES), it completes the collective control process.

[0077] In this way, when collective voltage adjustment is necessary and collective voltage adjustment is possible, the control circuit 400 adjusts the phase voltages of all phases collectively. On the other hand, when collective voltage adjustment is necessary and collective voltage adjustment is not possible, the control circuit 400 completes the collective control process without performing collective voltage adjustment. Furthermore, when collective voltage adjustment is not necessary, the control circuit 400 completes the collective control process without performing collective voltage adjustment. When the control circuit 400 completes the collective control process of step S105, the process returns to step S101.

[0078] In this embodiment, three-phase voltages are collectively adjusted by three-phase tap changing circuits 100 equipped with mechanical switches, and three-phase voltages are individually adjusted by three-phase semiconductor switching circuits 200 equipped with semiconductor switches. Therefore, according to the present disclosure, it is possible to adjust the balance of three-phase voltages at low cost. Note that the voltage adjusting device 1000 according to this embodiment takes time to switch the switches and has a slower operating speed than a TVR configured with semiconductor switches. However, the voltage adjusting device 1000 is intended to compensate for relatively gradual fluctuations in three-phase AC voltage, and therefore has a sufficient operating speed for this purpose.

[0079] Furthermore, the voltage regulator 1000 according to this embodiment can be created simply by adding the semiconductor switching circuit 200 to the tap changing circuit 100, which has the same specifications as the LTC provided in a general SVR. Therefore, the voltage regulator 1000 can be used without significantly changing the specifications of a general SVR.

[0080] In this embodiment, the primary winding 21 of the three-phase series transformer 20, the primary winding 31 of the three-phase regulating transformer 30, and the tertiary winding 33 of the three-phase regulating transformer 30 are each connected by a star connection. Therefore, the voltage adjustment device 1000 can apply a voltage that is in phase with the power distribution system, making voltage control easy. In other words, the voltage adjustment device 1000 can adjust only the voltage of the phase to be adjusted by simply switching the tap of the phase to be adjusted. Note that if at least one of the star connections of the above three star connections is replaced with a delta connection, switching the tap of the phase to be adjusted will affect the voltage of the phase not to be adjusted, requiring complex control.

[0081] (Variation) Although the embodiments have been described above, modifications and applications in various forms are possible. It is up to the discretion of the individual to adopt any of the configurations, functions, and operations described in the above embodiments. Furthermore, in addition to the above-described configurations, functions, and operations, additional configurations, functions, and operations may be adopted. Furthermore, the configurations, functions, and operations described in the above embodiments can be freely combined.

[0082] For example, in the embodiment, an example has been described in which the semiconductor switching circuit 200 is connected to one end of the primary winding 21 of the series transformer 20, and the tap changing circuit 100 is connected to the other end of the primary winding 21. Alternatively, the tap changing circuit 100 may be connected to one end of the primary winding 21 of the series transformer 20, and the semiconductor switching circuit 200 may be connected to the other end of the primary winding 21.

[0083] In the embodiment, an example has been described in which the number of taps that can be switched by tap changing circuit 100 is 9, and the number of taps that can be switched by semiconductor switching circuit 200 is 3. The number of taps that can be switched by tap changing circuit 100 may be 8 or less or 10 or more, and the number of taps that can be switched by semiconductor switching circuit 200 may be 2 or 4 or more.

[0084] The present disclosure allows various embodiments and modifications without departing from the broad spirit and scope of the present disclosure. Furthermore, the above-described embodiments are intended to explain the present disclosure and do not limit the scope of the present disclosure. That is, the scope of the present disclosure is defined by the claims, not the embodiments. Various modifications made within the scope of the claims and the meaning of equivalent disclosures are considered to be within the scope of the present disclosure. [Explanation of symbols]

[0085] P1, P2, P3 connection points U1, V1, W1 input terminals U2, V2, W2 output terminals 10, 10a, 10b, 10c Main circuit wiring 20, 20a, 20b, 20c Series transformers 21, 21a, 21b, 21c, 31, 31a, 31b, 31c, 41 Primary winding 22, 22a, 22b, 22c, 32, 32a, 32b, 32c, 42 Secondary winding 30,40 Regulating transformer 33, 33a, 33b, 33c Tertiary winding 100, 100a, 100b, 100c Tap changing circuit 101, 101a, 240 Mechanical switches 200, 200a, 200b, 200c, 201 semiconductor switching circuit 211,212,213,214,215,216,220 Semiconductor switches 230 resistor 300 Voltage detection circuit 400 Control circuit 1000 Voltage Regulator Circuit

Claims

[Claim 1] For each of the three phases in a distribution system that distributes three-phase voltage to loads, a series transformer having a primary winding and a secondary winding connected in series with the power distribution line; a regulating transformer including a primary winding connected to the distribution line, a secondary winding with multiple taps, and a tertiary winding connected in series with the primary winding and the secondary winding with multiple taps of the series transformer; a tap changing circuit including a mechanical switch for switching a tap connected to a primary winding of the series transformer among the plurality of taps provided on a secondary winding of the regulating transformer; a semiconductor switching circuit including a semiconductor switch for switching a connection state of a tertiary winding of the regulating transformer to a primary winding of the series transformer; a control circuit for collectively controlling the tap changing circuits for three phases to adjust the voltages of the three phases, and for individually controlling the semiconductor switching circuits for three phases to adjust the voltages of the three phases individually; Voltage regulator.

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